Drivers: hv: Extend/modify vmbus_channel_offer_channel for win7 and beyond

The "offfer" message sent by the host has been extended in win7 (ws2008 R2).
Add/modify state to reflect this extension. All these changes are backward
compatible.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>